(a) Technical Field
The present disclosure relates to a system and method for starting a fuel cell vehicle, particularly for starting a fuel cell vehicle in an emergency. More particularly, a system and method is provided for starting a fuel cell vehicle in an emergency in the event of a failure or malfunction of a high voltage system which can include a high voltage DC-DC converter and a high voltage battery.
(b) Background Art
As well known in the art, a hydrogen fuel cell vehicle employs a fuel cell system which comprises a fuel cell stack for generating electricity by an electrochemical reaction of reactant gases; a hydrogen supply system for supplying hydrogen as a fuel to the fuel cell stack; an air supply system for supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack; a thermal management system for removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management function; and a system controller for controlling the overall operation of the fuel cell system.
In a vehicle equipped with the fuel cell system, if the fuel cell is used as the only power source, the fuel cell powers all loads of the vehicle. This results in performance deterioration during operation when the efficiency of the fuel cell is low. Moreover, if a sudden load is applied to the vehicle, sufficient power often can not be supplied to a drive motor, which reduces the performance of the vehicle (for example, a sudden change in load imposes a heavy burden on the fuel cell since electricity is generated in the fuel cell by an electrochemical reaction).
Furthermore, a fuel cell has unidirectional output characteristics. Thus, if there is no separate storage means, it is difficult to recover energy from the drive motor during braking of the vehicle. As a result, efficiency of the vehicle system is decreased.
In an attempt to address these drawbacks, fuel cell hybrid vehicles have been developed. Such fuel cell hybrid vehicles preferably include both large vehicles such as buses as well as small vehicles. In addition to a fuel cell as a main power source, a fuel cell hybrid vehicle can be further equipped with a suitable storage means such as a high voltage battery or a supercapacitor as an auxiliary power source for providing suitable power required for driving the motor.
In particular, in a fuel cell-battery hybrid vehicle, a fuel cell used as a main power source and a high voltage battery used as an auxiliary power source are connected in parallel, and a low voltage battery (e.g., 12 V auxiliary battery) for driving low voltage components of the vehicle is further provided in addition to the high voltage battery (as a main battery). Accordingly, the fuel cell-battery hybrid vehicle can be equipped with two types of batteries such as the high voltage battery and the low voltage battery.
During start-up of the fuel cell, it is necessary to supply the fuel cell with air as well as hydrogen as reactant gases. However, high voltage components such as an air blower cannot be driven by the power of the fuel cell before the fuel cell reaches a normal operating state. Thus, oxygen-containing air is supplied to the fuel cell as an oxidant by driving the air supply system (e.g. air blower) by power from the high voltage battery in a state where a hydrogen supply valve (which starts and stops the hydrogen supply) is opened to supply the fuel cell with hydrogen (as a fuel) from a hydrogen tank.
FIG. 1 is a diagram illustrating the problems associated with the prior art. As shown, an electrical connection is provided between a fuel cell 10, an air blower 40, a high voltage DC-DC converter (HDC) 21 and a high voltage battery 20, which are used to supply power for driving the air blower 40 during start-up of the fuel cell 10. As shown in the figure, the fuel cell 10 and the high voltage battery 20 are connected in parallel to the air blower 40 as a high voltage component in a fuel cell system. A high voltage bus 30 is provided at an output side of the fuel cell 10. The high voltage battery 20 is further connected to an inverter 41 as a power module for rotating a motor M of the air blower 40.
In a typical fuel cell vehicle, it is necessary to supply power to the inverter 41 of the air blower 40 for supplying air (oxygen) to the fuel cell during start-up of the fuel cell 10. Thus, the high voltage of the high voltage battery 20 is boosted by the high voltage DC-DC converter 21, and is supplied to the inverter 41 of the air blower 40. Then, the inverter 41 inverts the phase of the voltage and drives the motor M of the air blower 40. As such, when the fuel cell 10 is started by driving the air blower 40 by the power of the high voltage battery 20, the air blower 40 is then driven by the power of the fuel cell 10 to supply necessary air to the fuel cell 10.
However, according to the above-described conventional fuel cell system, in the event of a failure or malfunction of a high voltage system, which includes the high voltage DC-DC converter 21 and the high voltage battery 20 (which drives the air blower 40 during start-up of the fuel cell 10), it is impossible to drive the air blower 40 to supply air to the fuel cell 10 during start-up, and thus the fuel cell 10 cannot be started.
In particular, according to such conventional systems, the drive power is supplied to the inverter of the air blower by the voltage output from the high voltage battery, and the voltage is boosted by the high voltage DC-DC converter during start-up of the fuel cell. Thus, the dependence on the high voltage system is absolutely high, which reduces the reliability of the system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.